Conventionally, in a semiconductor device having a semiconductor chip mounted on a mounting substrate, a chip capacitor for noise reduction is attached to a circuit board on which the semiconductor device is mounted. However, attaching the chip capacitor to the circuit board requires a long wire length between the semiconductor chip and the chip capacitor. This reduces the noise absorbing performance and hence degrades the performance as a decoupling capacitor. This also prevents the miniaturization of the semiconductor device as a whole including the chip capacitor.
To solve these problems, it has been tried to miniaturize semiconductor devices by providing an interposer with a built-in capacitor or by interposing an element having a capacitor function between the mounting substrate and a semiconductor chip.
For example, Japanese Patent Unexamined Publication No. 2001-326305 (hereinafter, Patent Document 1) discloses the following structure.
In Patent Document 1, an interposer is provided with capacitors on a surface thereof that is opposite to the surface having protruding electrodes thereon. This structure enables the capacitors integrated into the interposer to be disposed right under the semiconductor chip, making it possible to fully function as the decoupling capacitors. It is also possible to produce the plurality of capacitors at the same time as the interposer, making the production cost low.
Japanese Patent Unexamined Publication No. 2003-142624 (hereinafter, Patent Document 2) discloses a method for producing an interposer with built-in passive elements such as a bypass capacitor. The method includes a process of forming an interposer with built-in passive elements on a base substrate; a process of mounting at least one semiconductor chip on the interposer formed on the base substrate; a process of separating the base substrate from the interposer so as to expose the other surface of the interposer; and a process of mounting the interposer on a mounting substrate via an electrode pad exposed on the other surface of the interposer.
In this production method, the interposer is fixed to the base substrate until the semiconductor chip is mounted on the interposer, so that the interposer is reinforced by the base substrate. Even after the base substrate is removed, the semiconductor chip mounted on the interposer performs the reinforcement function. This provides a thin interposer with a built-in bypass capacitor while preventing the interposer from deformation or damage during the production process.
Japanese Patent Unexamined Publication No. 2004-55769 (hereinafter, Patent Document 3) discloses a semiconductor device including a mounting substrate; a semiconductor chip mounted thereon; and a capacitor allowing the semiconductor chip to operate stably at a high frequency range. The capacitor is electrically connected to an electrode pad disposed on the bottom surface of the semiconductor chip. The substrate having the capacitor thereon has a thickness equal to or less than the height of the protruding electrodes of the semiconductor chip. The capacitor is formed on the smooth surface of the substrate made of silicon, glass, or the like. The capacitor is polished from the substrate side so as to make the thickness of the substrate equal to or less than the height of the protruding electrodes when the semiconductor chip is mounted on the mounting substrate. This results in the minimization of the wire length between the semiconductor chip and the capacitor.
In Patent Document 1, the capacitors are produced at the same time as the interposer. The capacitors are made of STO (strontium titanium oxide) or the like.
STO, however, needs to be made at comparatively high temperatures in order to obtain good dielectric properties and also requires that the insulation base material has a smooth surface. This makes it necessary that the insulation base material is made not of resin base material generally used for printed-circuit boards, but of silicon, glass, polyimide resin, or the like. Moreover, forming the capacitors, throughholes, wiring patterns, and the like on the insulation base material makes the production process complicated and makes it difficult to obtain a high yield.
In Patent Document 2, on the other hand, the interposer with the built-in capacitor is formed on the base substrate, and the semiconductor chip is mounted on the interposer. After this, the interposer from which the base substrate has been removed is mounted on the mounting substrate. Thus, the interposer needs to have the capacitor in addition to throughholes and wiring patterns required for the interposer. To achieve this structure, the base substrate is made of a silicon substrate, and the dielectric film for the capacitor is made of a BST film (a barium strontium titanium oxide film). As a result, the interposer of Patent Document 2 also requires a complicated production process and the yield is low.
In Patent Documents 1 and 2, the capacitors are built in the interposer; however, the process of producing the interposer is so complicated that the yield is low, making it impossible to produce the interposer at low cost.
In Patent Document 3, on the other hand, the thin film capacitor is interposed between the semiconductor chip and the mounting substrate. In other word, the substrate having the thin film capacitor only thereon is interposed between the semiconductor chip and the mounting substrate, thereby simplifying the production process.
Since, however, the thin film capacitor is formed on a silicon substrate or a glass substrate, it is necessary to precisely control the height of the protruding electrodes of the semiconductor chip and the thickness of the silicon substrate on which to form the thin film capacitor. When the silicon substrate on which to form the thin film capacitor is thick, the semiconductor chip may be damaged at the surface having a circuit thereon when a force is applied during flip-chip mounting. Moreover, it is difficult to securely fill underfill resin between the semiconductor chip and the mounting substrate, thereby deteriorating the reliability.